Cell Structure and Composition Quiz

Cell Structure and Composition

• Cells are the basic structural and functional units of all life forms.
• Study of structure and composition of cells is called Cytology.

Discovery of Cells

• Robert Hooke first observed cells in a dead cork slice in 1665.
• He described his findings in his book "Micrographic".
• The word "cell" was derived from the Greek word "Cellulae", meaning small room.
• The first living cell was discovered by A.V. Leeuwenhoek.

Protoplasm

• Protoplasm was coined by Purkinje in 1839.
• It was discovered by Felix Dujardin and named as sarcode.
• Protoplasm has varying consistency under different conditions and exists in sol-gel states.
• It is an aggregate of various chemicals such as water, ions, salts, and other organic molecules like proteins, carbohydrates, fats, nucleic acids, vitamins, etc.

Cell Theory

• The cell theory was given by Schleiden and Schwann, and later expanded by Rudolf Virchow.
• The cell theory states that:
  • All plants and animals are composed of cells.
  • Cell is the basic unit of life.
  • All cells arise from pre-existing cells.
• Viruses are an exception to the cell theory.

Types of Cells and Organisms

• On the basis of the number of cells, organisms can be categorized as:
  • Unicellular organisms (e.g. Amoeba), which are made up of a single cell that performs all vital body functions.
  • Multicellular organisms (e.g. plants and animals), which are made up of numerous cells that combine to form organs and organ systems.
• On the basis of the type of organization, cells can be categorized as:
  • Prokaryotic cells (e.g. Bacteria), which are primitive and incomplete cells with less developed nuclei without nuclear membrane and nucleolus.
  • Eukaryotic cells (e.g. Plants and animals), which are well-developed cells with advanced nuclei with nuclear membrane and nucleolus.

Cell Shape and Size

• Cells have variable shapes and sizes, with shapes dependent on their function.
• Cells can be spherical, elongated (nerve cell), branched (pigmented), discoidal (RBC), spindle-shaped (muscle cell), etc.
• The size of cells varies depending on the type of organism, ranging from 0.2 µm to 18 cm.
• A typical cell in a multicellular organism ranges from 20-30 µm in size.
• The largest cell is the ostrich egg, with a diameter of 15 cm (with shell) and 8 cm (without shell).